" Indeed ProxySQL doesn’t support caching_sha2_password authentication plugin, but since ProxySQL 2.0.3 (March 2019) a client connection using caching_sha2_password will be automatically switched to mysql_native_password. With regards to “OPT_CHARSET_NAME=utf8”, the problem is that your backend it is not MySQL 8.0 : the client is trying to use a charset (likely utf8mb4_0900_ai_ci) that the backend doesn’t support. ProxySQL 2.0.9 automatically fixes this, switching to the default charset defined in mysql-default_charset."

Password Authentication Plugin

Default Charset Configuration

mysql> SELECT @@version, @@hostname;
 +------------+------------+
 | @@version | @@hostname |
 +------------+------------+
 | 5.7.29-log | mysql1 |
 +------------+------------+
 1 row in set (0.00 sec)
 
 mysql> SHOW COLLATION WHERE Charset = 'utf8mb4';
 +------------------------+---------+-----+---------+----------+---------+
 | Collation | Charset | Id | Default | Compiled | Sortlen |
 +------------------------+---------+-----+---------+----------+---------+
 | utf8mb4_general_ci | utf8mb4 | 45 | Yes | Yes | 1 |
 | utf8mb4_bin | utf8mb4 | 46 | | Yes | 1 |
 | utf8mb4_unicode_ci | utf8mb4 | 224 | | Yes | 8 |
 | utf8mb4_icelandic_ci | utf8mb4 | 225 | | Yes | 8 |
 | utf8mb4_latvian_ci | utf8mb4 | 226 | | Yes | 8 |
 | utf8mb4_romanian_ci | utf8mb4 | 227 | | Yes | 8 |
 | utf8mb4_slovenian_ci | utf8mb4 | 228 | | Yes | 8 |
 | utf8mb4_polish_ci | utf8mb4 | 229 | | Yes | 8 |
 | utf8mb4_estonian_ci | utf8mb4 | 230 | | Yes | 8 |
 | utf8mb4_spanish_ci | utf8mb4 | 231 | | Yes | 8 |
 | utf8mb4_swedish_ci | utf8mb4 | 232 | | Yes | 8 |
 | utf8mb4_turkish_ci | utf8mb4 | 233 | | Yes | 8 |
 | utf8mb4_czech_ci | utf8mb4 | 234 | | Yes | 8 |
 | utf8mb4_danish_ci | utf8mb4 | 235 | | Yes | 8 |
 | utf8mb4_lithuanian_ci | utf8mb4 | 236 | | Yes | 8 |
 | utf8mb4_slovak_ci | utf8mb4 | 237 | | Yes | 8 |
 | utf8mb4_spanish2_ci | utf8mb4 | 238 | | Yes | 8 |
 | utf8mb4_roman_ci | utf8mb4 | 239 | | Yes | 8 |
 | utf8mb4_persian_ci | utf8mb4 | 240 | | Yes | 8 |
 | utf8mb4_esperanto_ci | utf8mb4 | 241 | | Yes | 8 |
 | utf8mb4_hungarian_ci | utf8mb4 | 242 | | Yes | 8 |
 | utf8mb4_sinhala_ci | utf8mb4 | 243 | | Yes | 8 |
 | utf8mb4_german2_ci | utf8mb4 | 244 | | Yes | 8 |
 | utf8mb4_croatian_ci | utf8mb4 | 245 | | Yes | 8 |
 | utf8mb4_unicode_520_ci | utf8mb4 | 246 | | Yes | 8 |
 | utf8mb4_vietnamese_ci | utf8mb4 | 247 | | Yes | 8 |
 +------------------------+---------+-----+---------+----------+---------+
 26 rows in set (0.00 sec)
 
 
 So once again as René mentioned in his comment ProxySQL 2.0 has a solution for this namely the setting mysql-default_charset. In my test environment this is set to the default value 'utf8'.
 
 Admin> SELECT @@version;
 +--------------------+
 | @@version |
 +--------------------+
 | 2.0.10-27-g5b31997 |
 +--------------------+
 1 row in set (0.00 sec)
 
 Admin> SHOW VARIABLES LIKE 'mysql-default_charset';
 +-----------------------+-------+
 | Variable_name | Value |
 +-----------------------+-------+
 | mysql-default_charset | utf8 |
 +-----------------------+-------+
 1 row in set (0.01 sec)

Once again, as René mentioned in his comment, ProxySQL 2.0 has a solution for this (namely the 

setting).
 
 In my test environment, this is set to the default value 'utf8'. 

Admin> SELECT @@version; 
 +--------------------+ 
 | @@version | 
 +--------------------+ 
 | 2.0.10-27-g5b31997 |
 +--------------------+ 
 1 row in set (0.00 sec) 
 
 Admin> SHOW VARIABLES LIKE 'mysql-default_charset';
 +-----------------------+-------+ 
 | Variable_name | Value | 
 +-----------------------+-------+ 
 | mysql-default_charset | utf8 | 
 +-----------------------+-------+ 
 1 row in set (0.01 sec)

SSL All the Things!

Admin> SELECT hostgroup_id, hostname, use_ssl FROM mysql_servers;
 +--------------+-------------+---------+
 | hostgroup_id | hostname | use_ssl |
 +--------------+-------------+---------+
 | 100 | 192.168.0.2 | 0 |
 | 101 | 192.168.0.3 | 0 |
 | 101 | 192.168.0.4 | 0 |
 +--------------+-------------+---------+
 3 rows in set (0.01 sec)
 
 Admin> UPDATE mysql_servers SET use_ssl = 1;
 Query OK, 3 rows affected (0.00 sec)
 
 Admin> LOAD MYSQL SERVERS TO RUNTIME;
 Query OK, 0 rows affected (0.00 sec)
 
 Admin> SAVE MYSQL SERVERS TO DISK;
 Query OK, 0 rows affected (0.06 sec)
 
 Let's verify if our backend connection is using SSL
 
 $ mysql -h192.168.56.2 -P33061 -uapp_rw -p
 Enter password:
 Welcome to the MySQL monitor. Commands end with ; or \g.
 Your MySQL connection id is 10
 Server version: 5.5.30 (ProxySQL)
 
 Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
 
 Oracle is a registered trademark of Oracle Corporation and/or its
 affiliates. Other names may be trademarks of their respective
 owners.
 
 Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
 
 mysql> SHOW SESSION STATUS LIKE "Ssl_cipher";
 +---------------+---------------------------+
 | Variable_name | Value |
 +---------------+---------------------------+
 | Ssl_cipher | DHE-RSA-AES256-GCM-SHA384 |
 +---------------+---------------------------+
 1 row in set (0.00 sec)
 
 mysql>

However, the frontend connection is not yet using SSL.
 

mysql> \s
 --------------
 mysql Ver 14.14 Distrib 5.7.22, for osx10.12 (x86_64) using EditLine wrapper
 
 ...
 Current user: app_rw@192.168.0.8
 SSL: Not in use
 ...
 
 Time to enable frontend SSL. The ProxySQL manual again teaches us to set the variable mysql-have_ssl to true (default value is still false). Let's try:
 
 Admin> SHOW VARIABLES LIKE 'mysql-have_ssl';
 +----------------+-------+
 | Variable_name | Value |
 +----------------+-------+
 | mysql-have_ssl | false |
 +----------------+-------+
 1 row in set (0.00 sec)
 
 Admin> SET mysql-have_ssl = 'true';
 Query OK, 1 row affected (0.00 sec)
 
 Admin> LOAD MYSQL VARIABLES TO RUNTIME;
 Query OK, 0 rows affected (0.00 sec)
 
 Admin> SAVE MYSQL VARIABLES TO DISK;
 Query OK, 143 rows affected (0.01 sec)
 
 Admin> SHOW VARIABLES LIKE 'mysql-have_ssl';
 +----------------+-------+
 | Variable_name | Value |
 +----------------+-------+
 | mysql-have_ssl | true |
 +----------------+-------+
 1 row in set (0.00 sec)

Conclusion